PORTLAND, Ore. (AP) _ The mighty laser printer, a staple of modern-office machinery, is losing ink to an inexpensive computerized rival that sprays words and images onto a page in bold color.

''Inkjet'' printers commanded only 10 percent of the market last year, but are expected to overtake laser printers as soon as 1994.

''Years ago, when the desktop computer era was just beginning, people said inkjet printers would be the way to go and laser printers would never fly,'' said Marc Boer, a senior analyst with International Data Corp. in Boston, a market research company.

Hewlett-Packard, the U.S. computer and scientific instrument giant, has spent millions of dollars nurturing inkjet technology since the early 1980s.

The company is poised for a major trade battle with its main rival in the computer printer market, Canon Inc., the Japanese company that builds the components for more than three-fourths of the world's laser printers.

Canon, which already has its own version of the inkjet printer, agrees that inkjets are the wave of the future.

''It may sound ironic that the longtime leader in laser printers is saying inkjet technology will become more important, but it's not that laser printers will fade away. It's just that inkjet technology is accelerating very, very quickly,'' said Peter Bergman, marketing chief for Canon Computer Systems, a Canon subsidiary in Costa Mesa, Calif.

The computer printer market was worth $8.4 billion in North America in 1991, according to figures compiled by Dataquest Inc., a market research company in San Jose, Calif.

The market share for inkjets will jump as more small businesses and consumers buy inexpensive but sophisticated desktop computers, only to find they need equally inexpensive and sophisticated printers, said Dataquest spokesman John Goetz.

The key advantages of inkjets are their simple, reliable design and low cost. The H-P DeskJet model, built at a plant in Vancouver, Wash., sells for less than $400, compared to $700 to $1,000 for a typical ''low-cost'' laser printer.

Most of the price difference comes from the difference in technologies.

An inkjet printer uses a small computer chip sealed into a disposable cartridge with tiny nozzles that spray microscopic droplets of ink onto a piece of paper to create letters or graphics. It needs little power or space, and if something goes wrong with the print head, you just throw it away and snap in a new one.

A laser printer uses technology similar to a copying machine. It charges a piece of paper electrically to attract tiny particles of powdered ink called toner into the shapes of letters or graphics that are melted onto the page. The mechanism is bulky, complex, power-hungry and expensive to repair.

The other main advantage of inkjet printers is the ability to print in color cheaply. Color laser printers, like color copiers, are extremely expensive.

''I would expect almost an exponential growth for color inkjets,'' said Mark Hanley, co-founder of IT Strategies in Boston, a marketing research and analysis firm.

Hanley, who has worked extensively in Europe, says the inkjet technology was more readily accepted in Europe and Asia, where early problems with the quality of printed documents was not the critical issue that turned businesses toward laser printers in the United States.

The arrival of cheap color inkjet printers with much-improved quality comes at a time of growing demand for color highlights and graphics in business documents in the United States, meaning that many aging monochrome laser printers may be replaced, Hanley says.

It also almost surely spells the end for the dot-matrix printer, a noisy modern version of a teletype machine that has survived mostly because it was the cheapest alternative to laser printers, Hanley and other analysts say.

The chief manufacturer of dot-matrix printers worldwide, Epson, already has plunged into the inkjet market with its own variation of the technology, announced in November.

The company had been developing inkjet printers but had delayed introduction until the market was receptive, says Rob Rosborough, who is leading Epson's effort from its U.S. headquarters in Torrance, Calif.

''We don't bring our products to the market until they begin to penetrate the mainstream,'' Rosborough said. ''The mainstream for inkjet printers is when the price begins dropping below $400. That's where things are at right now.''